Squelch circuit



May 12, 1953 G. K. JENSEN ETAL SQUELCH CIRCUIT Filed July 14, 1945 UTILIZATION NET WORK gwoe/wbow GAROLD K. JENSEN JACOB BENVENISTE neet qn Patented May 12, 1953 "ensues; I

I 'A 'pplicatiqn ,-.'-.I:his intentien; re ateecto a means t nem tiyelyz disa lin .a radio renewing system when the-in ent SlfibfilJLD-ltfifiihdlgflfi below acertein eredeterminedminimumvalue. in inventien the. he t at which. the die sibling; .er: squemhine ei enit: eomes inmopera: th n-is seleetednnithe basiaef the. minimumrsige 1nd level at-whichthereeeived si el e. intelli ible. Wer -the. noise. pied-need; either in there; 661E612 ori by. interfering signal" sources ..In ne tienlar, the, present system is. usefuhin eliminatr .ing noise.- which. WOuld qtherwise be'objeetioname whentunin v .frem one statien to. anotherorin afibreakeinhoperation. An abject ofthisnmvention istherefere teem, hide a; eireui for disablin a r newing est tem when the m mum peak. oiithereeeived ignal falls tale predetermined;m n m mletei .c

. A. inrtherohieet nfthis. .inventienis te. nroxide inca. radio pulse receive-ref the type which em plays aresonantcireuitfer transforming periodic .nulseesignals. inter, a sine wave, a. .eimnit w itb will damnthe ,osciHat-iens qecurrina in the reed nantcireuit whenthe received pulse, signals drop rheldwa predeterminediyalue, c. e Other Objects. and features of thecgresent. in: rentionvvtill become ,anparentupen arcareful can? eideration .cf. the, renewing. detailed deeeription when [taken A v. togetherv with. uthe aeeom nnyin drawings, the sin le fi ureefzwhieh is. ill stratiire of eneembediment,oftheinrentioni With reference \tncthe drawing; a pulse receiver; system employin a squeleh n aim-n 'cnnstrncted according: .to.. the .nrineiple i the present invention is; diselosed. .c .Ferpurne es of illustration the .squelchin circuit is shawn "as nnenatingin nonjunction. with the receiving .equinment or a pulse irequeney medulatiqn sye temisuch. as that disclosed ineureqnendine an? plication, 1 entit1ed,- :Qemmunieatien fiv etemfi SerialLNn 6%,168 filed July 14, 1M5, new Patent Ne. 2,58QA3L, ,r c H 1. M

,(Radiqufrequem y signals, emitted by a. distant transmitter,.are. receive.d by the. antenna .10 and are :amnlifiedand detected by a suitable numher at preamplifier sta es indicated neral .1 I. Included. .in;the. circuit ,li hutinet strewn/may be a, noise gating circuit which functiqnajohper mitnan nutput from-oircuit ll only during the arrivaltofa desirednulse signal. Such a means is disclosed in the aforementioned patent applicatiennn'lhere mayi alsb be included in the'design of the l -t'a sui tahl g limiter stage whiqhis arranged so that all s ignals'impinging n npqnthe antenna l andeireeeding a'ce I predetermined level'appear at the output with rinifbrrnpositive amplitude; Tube 1 which; thequtput-of thecircuit ll is agp biased near cutoff 'by'means ef s' cathege ente' the juncture 'peinte resist I and l! which are int-urnconnc'ted bet; and greundr Outputpulsesfreniftube ;I

across its plate-load resistance and am Staten New 1945, SeriafNu. sometne ati emltaee p lees, .Tlhe. nea e pu se-signals whi h anseethe a id t nvememe the, ca bed bias te1tag .=.on tube .tzcwill eausereet'ned grid eurrentte. ne with the; esult tha the. enn ine e negativ ly Between a e he eereeit nee t. dis hnraes na .ree staneee H and U eenneet: 1;

strenethe f the a mp n n en new taer lii be here natter.deee leed, t e to teeecenr etinet at, the iu ettr pe nt ef .r sistene s Ml need. the, purp se, or .gqnt

' time the and lli e .r h ueleh; a c rcuit, ermin e e eentrei e aee e d, by. the hee s ee siena e ar b ien t it. le el; e blieh dbnthea erement V c sta e ei ir nit t, a .e pneiteneeifi e ne ee h txreenthe iu e i npe nt 9i; ree stanee H n annexe The he-qen l t. it Wen th tthe't me ees nt, th tit terms th resistante, ill evera -2- ;e' te. han he e n ne ri e he. an N d ei 4 g, stems is the ease Wherethe r e 7 adapted to operate on p ulse frequency mpd i lae time 16, an iiniiitikar 19% m? Y -@Q i zi m y h rerted mm a req en s; m dulat d, s ne w Eertl i flrr se a tuned ireuitlqemn. me duetan e- 3 a d eapee tanee z t-and ad ed t t of tube l2 may be, for example,

.glate e enit 9f aseeend ampl fi r new 5, his a, ti r ieb sed normally eendu ma by mean new ca hode. r si tance 2L. rn e r uit itself. i selected to "r semt 'the ate .pr s i exam le. a l mit st g a fi qu n y d1 ce n nate t. aud o ammifienend n ud rep duqing deyi-cdall" of'ccnventidnai design, c' 'nected tqg ether in the crder given.

lril lcontigil ingj a squelching circuit froni' a sou ce of vqltagegenerated at the receiverin'responsetp thereceived pulses-finals, suchas that pi'dduced at the juncture qf res i'stances l1 and 18 it is apparentthat the squeic-hing circuiti-tself 1mm be situated at a stage subsequent tad'the point where the control' voltage is develepedi In the present ease it has been found advantaeeeus to" insert the squel'ching circuit at the pulse to Sine wave conversion stage 2H1 Fonsquelching 'pur-pbses fa; suitable amplifier tube" 25' functioning a's a" variable resistance element is connected ifi shiifit Wifih'fiube 201 The of'fub 25 is'retilihddifbtl? td'the'juncwm 0f sistance of this potentiometer is connected berttween B+ and ground. In normal operation the bias on tube 25 is adjusted by the movable tap on potentiometer 21 so that when the peak input signal being received is unintelligible over the noise the negative voltage developed :at-the juncture point of resistances H and i8 rises posi. tively to a point, controllable by potentiometer 21 As conductionby tube n where tube 25 conducts.

25 takes place a large current is caused to flow through both resistance 22, which is inserted in the plate of tube 29 and the inductance'of the tuned circuit consisting of inductance 23 and capacitance 24. This current both lowers the voltage at the plate of tube by reason of the voltage drop through resistance 22 and loads the tuned circuit so as to prevent the pulse signal from the output of tube 12 from exciting oscillations therein. As the peak signal level increases to its normal level, the voltage at the juncture point of resistances I1 and i8 increases negatively to cut off tube 25. This action effectively removes the highly dissipative unilateral current component drawn by tube 25 through inductance 23 thereby permitting rapid build-up of the oscillations in the tuned circuit 39. From the foregoing it is apparent that a number of modifications of the basic circuit may be made without exceeding the spirit of the invention. For example, in the case where other types of pulse modulation systems are employed the stage to which the squelching circuit is connected is immaterial as long as the squelching circuit operates to-suiiiciently reduce the stage gain to suppress the receiver output. Therefore this invention is not to be limited except as is necessitated by the prior art and the spirit of the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalt thereon or therefor.

What is claimed is:

1. In a pulse energy operative device, a pulse energy source providing recurrent pulses of vari able amplitude, a resonant circuit connected to the pulse energy source to produce sinusoidal oscillations in response to said pulses, an energy dissipative device connected to the resonant cir- :into a frequency modulated sinusoidal waveform,

a resonant circuit tuned to the average recur- .rence frequency of said pulses, electron tube driver means applying the input pulses to said resonant circuit, damping means connected to said resonant circuit, a peak detector including a time constant circuit having a time constant greater than the recurrence period of said pulses, said peak detector being coupled between the input side of said driver means and said damping means'torender the damping means inoperative when the average amplitude of the input pulses maintains at least a selected minimum level.

4. In a receiving device for converting frequency modulated input pulses whose amplitudes may vary into a frequency modulated sinusoidal waveform, a resonant circuit tuned to the average recurrence frequency of said pulses, electron tube driver means applying the input pulses to said resonant circuit, an electron tube energy dissipating element connected to said resonant circuit, a peak detector including a time constant circuit having a time constant greater than the recurrence period of the pulses, said peak detector being coupled between the input side of said driver tube and electron tube energy dissipating element to render the electron tube dissipating element inoperative when the average amplitude of the input pulses maintains at least a selected minimum level.

5. In a receiving device for converting frequency modulated input pulses whose amplitudes may vary into a frequency modulated sinusoidal waveform, a resonant circuit tuned to the average recurrence frequency of said pulses, electron tube driver means applying the input pulses to said resonant circuit, an electron tube energy dissipating element connected to said resonant sipating element non-conductive when the average amplitude of the input pulses maintains at least a selected minimum level.

6. In a receiving device for converting frequency modulated input pulses whose amplitudes may vary into a frequency modulated sinusoidal cult, and a peak detection circuit coupling said pulse energy source to said energy dissipative device operative to produce heavy damping of the resonant circuit except when pulses from the energy source have at least a preselected minimum amplitude.

2. In a receiving device for converting frequency modulated input pulses whose amplitudes may vary into a frequency modulated sinusoidal Waveform, a resonant circuit tuned to the averag recurrence frequency of said'pulses, in-

put means applying the input pulses to said resonant circuit, damping means connected to said resonant circuit, a peak detector including a time constant circuit having a time constant greater than the recurrence period of the pulses, said 7 waveform, a resonant circuit tuned to the average recurrence frequency of said pulses, driver means applying the input pulses to said resonant circuit, an electron tube and a resistance serially connected with said resonant circuit, a peak detector including a time constant circuit having a time constant greater than the recurrence period of said pulses, said peak detector being coupled between the input side of said driver means and said electron tube to render said tube nonconducting when the average amplitude of the input pulses maintains at least a selected minimum level.

GAROLD K. JENSEN. JACOB BENVENISTE.

References Cited in the file of this patent UNITED STATES PATENTS Name 

